With the rise of smartphones, the demand for high-quality sound and compact design has grown. Technologies such as noise suppression and echo cancellation have been widely adopted to enhance audio quality.
Principle of Capacitive MEMS Microphones
MEMS microphones are miniature sensors that operate based on sound-induced force gradients. The diaphragm undergoes deformation due to sound pressure changes, leading to variations in capacitance between the diaphragm and the silicon backplate.
This capacitance variation is converted into a voltage signal through a capacitance-to-voltage circuit, and the MEMS sensor amplifies the output voltage. A high-impedance resistor provides a bias voltage (VPP) to stabilize the charge within the MEMS sensor. The final output voltage is proportional to both VPP and the diaphragm deformation.
CMOS MEMS Microphone Circuit Design
In CMOS MEMS microphones, the circuit design plays a crucial role in sensor operation, sensitivity, and overall system performance.
Electret condenser microphones (ECMs) use electret material to generate a static charge, whereas MEMS microphones extract a bias voltage from the CMOS operating voltage and apply it to the diaphragm via a high-impedance resistor.
MEMS Microphone Fabrication Methods
- Pre-CMOS MEMS: MEMS structure is fabricated before CMOS components.
- Intra-CMOS MEMS: CMOS and MEMS structures are manufactured together.
- Post-CMOS MEMS: CMOS components are fabricated first, followed by MEMS structure formation.
Advantages of MEMS Microphones
MEMS microphones have replaced ECMs in many applications due to their superior durability, compact size, and ease of digital integration.
- Stable Performance: Made from semiconductor materials, MEMS microphones are unaffected by temperature and humidity changes.
- High-Temperature Resistance: Unlike ECMs, MEMS microphones can withstand reflow soldering temperatures of up to 260°C.
- Digital Signal Processing: Digital MEMS microphones support noise cancellation, beamforming, and echo suppression for improved voice communication quality.
Applications
MEMS microphones are widely used in smartphones, laptops, and voice-controlled set-top boxes. As digital audio processing continues to evolve, MEMS technology is expected to expand into more consumer and industrial applications.
